This invention relates to a rack assembly for a mine winning machine drive arrangement, the rack assembly being associated with a longwall conveyor along which a mine winning machine is movable by the drive arrangement.
In order to move a mine winning machine (such as a shearer) to and fro along a longwall conveyor, it is known to mount a rack assembly having drive apertures on the conveyor, and to drive the machine along the rack assembly using a drive element which engages with the drive apertures. The rack assembly is constituted by a plurality of rack sections which are connected, by means of of horizontal bolts, to the channel sections of the longwall conveyor in such a manner as not to interfere with the necessary horizontal and vertical articulation movements of the channel sections. With a drive arrangement of this kind, it is difficult to avoid excessively great errors in the pitch of the drive apertures of the rack assembly at the regions where the rack sections adjoin each other, which errors are caused by the articulation movements of the channel sections. At the same time, however, the articulation movements of the channel sections should not be unnecessarily limited. As is well known, vertical articulation movements of the channel sections are necessary for adjusting the longwall conveyor to compensate for variations in the level of the floor of a mine working; whereas horizontal articulation movements of the channel sections are necessary to permit the conveyor to be advanced in sections, in what is known as a "snaking" advance movement. The articulation of the channel sections in the vertical plane is generally required to be greater than in the horizontal plane.
The rack sections may be arranged in such a way that they bridge the zones where the conveyor channel sections adjoin each other by a distance equal to half their length. This arrangement enables the articulation angle of the channel sections at the zones where the rack sections adjoin to be reduced, and thus leads to a reduction in the errors in the pitch of the drive apertures at these zones. In this system, the rack sections have a length which is either equal to, or less than, the length of each channel section. (See U.S. Pat. No. 4,082,361).
In a further development of the above-mentioned drive arrangement provision is made for permitting the rack sections to move longitudinally to a limited extent on the longwall conveyor with the aid of bolt-and-slot connections; and for using rack sections each having a convex face at one end and a complementary concave face at the other, so that the rack sections bear against each other at the end faces, and can move relatively to each other in the manner of a hinge. This arrangement is intended to ensure that, given adequate articulation of the channel sections in the vertical and horizontal planes (even when the longwall conveyor is moving along an arcuate path and undergoes vertical deflections), the minimum pitch dimension of the rack sections is not fallen short of to such extent that the drive element (a driven pinwheel) of the winning machine is unable to find a gap for the engagement of its teeth between the rack sections at the zones where the rack sections adjoin each other. (see DE-PS No. 2 646 291).
It is also known to attach the rack sections to the channel sections of the conveyor in an alternating sequence, wherein a first pair of rack sections are rigidly interconnected and the next pair have motional play in their longitudinal direction, and so on. This arrangement is aimed at eliminating, or reducing, the load on the support members for the rack sections, which load is caused by the articulation of the channel sections in the vertical and horizontal planes. (See DE-OS No. 2 721 867).
The aim of the invention is to provide a rack assembly having rack-attachment means that is particularly simple to construct and assemble and is at the same time stable; and to provide a rack assembly having individual rack sections which have great relative mobility to accommodate the required vertical and horizontal articulation of the channel sections, without the errors in pitch at the zones where the rack sections adjoin becoming undesirably great.